IFN-gamma-induced TNF-alpha is a prerequisite for in vitro production of nitric oxide generated in murine peritoneal macrophages by IFN-gamma.

The effect of IFN-gamma to stimulate formation of nitric oxide (NO) by normal murine peritoneal macrophages (M phi) has been found to be completely dependent on the ability of IFN-gamma to activate secretion of TNF-alpha. The NO-stimulatory effect of IFN-gamma was abolished by anti-TNF-alpha antibodies, the inhibitory intervention of which could be fully reversed by exogenously supplied TNF-alpha. Accordingly, the failure of M phi from C3H/HeJ mice to secrete TNF-alpha upon stimulation with IFN-gamma was associated with their complete incapability to generate NO, unless they were simultaneously treated with IFN-gamma + TNF-alpha. Collectively, the data document that similar to the NO up-regulatory action of other cytokines, the effect of IFN-gamma is not independent, but depends on a synergistic cooperation with the self-produced TNF-alpha. The findings thus indicate that a widespread opinion claiming that IFN-gamma per se is able to stimulate biosynthesis of NO needs revision.